1. Field of the Invention
The present invention relates in general to a magnetic transfer master medium provided on the surface thereof with protrusion portions formed in a pattern for transmitting data to a magnetic recording medium, and in particular to a magnetic transfer master medium for transferring data to a perpendicular magnetic recording medium.
Further, the present invention relates to a magnetic transfer method of employing the magnetic transfer master medium according to the present invention to transfer data to a perpendicular magnetic recording medium, and a magnetic transfer master medium forming method.
2. Description of the Related Art
Generally speaking, with regard to magnetic storage mediums, there is a demand for increased storage capacity and low cost. Further desired are so-called high-speed access mediums, which are capable of advantageously reading out the data of a desired location in a short time. Examples of these mediums include the high speed magnetic recording mediums (magnetic disk mediums) utilized in hard disk apparatuses and flexible disk apparatuses. So-called tracking servo technology, wherein the magnetic head accurately scans a narrow width track to achieve a high S/N ratio, plays a substantial role in attaining the high storage capacity thereof. A servo signal, address data signal, replay clock signal, etc., used for tracking within a certain interval occurring in one rotation of the disk are “preformatted”, that is, recorded on the disk in advance.
Magnetic transfer methods realizing accurate and efficient preformatting, wherein the data such as a servo signal or the like borne on a master medium is magnetically transferred therefrom to a magnetic recording medium, have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566.
According to these magnetic transfer technologies, a master medium having an uneven pattern corresponding to the data that is to be transferred to a slave medium (a magnetic recording medium) is prepared. By bringing this master medium brought into close contact with a slave medium to form a conjoined body, and applying a transfer magnetic field thereto, a magnetic pattern corresponding to the data (e.g., a servo signal) borne on the master medium is transferred to the slave medium. The preformatting can be performed without changing the relative positions of the master medium and the slave medium; that is, while the two media remain stationary. Therefore not only is it possible to perform an accurate recording of the preformat data, it becomes possible to advantageously do so in an extremely short time.
However, as to the magnetic recording medium, two possibilities are longitudinal magnetic recording mediums provided with an easy magnetization axis in the horizontal direction in relation to the surface of the magnetic layer thereof, and perpendicular magnetic recording mediums provided with an easy magnetization axis in the vertical direction in relation to the surface of the magnetic layer thereof; however, in current practice, longitudinal magnetic recording mediums are generally employed, and the magnetic transfer technology described above has also been developed focusing mainly on the longitudinal magnetic recording mediums as the magnetic recording medium of choice. On the other hand, if a perpendicular magnetic recording medium is employed, an increase in data storage capacity can be expected in comparison to the longitudinal magnetic recording mediums.
For cases in which a magnetic transfer is performed on a perpendicular magnetic recording medium, a magnetic field must be applied in the perpendicular direction with respect to the surface of the magnetic layer thereof; wherein the optimal conditions differ in contrast to cases in which a magnetic transfer is performed on a longitudinal magnetic recording medium.
For example, when a magnetic transfer is performed to a perpendicular magnetic recording medium, the magnetic disorder is large at the border portions between the inverse magnetization portions and the uninverted magnetization portions, wherein a problem arises in that the signal quality is not favorable. Based upon the analysis by the inventors of the present invention, it has become clear that this problem is due to an insufficient constraint of the magnetic flux of the inverse magnetization portions, and is the cause of a reduction in signal quality.
Further, when a perpendicular magnetic transfer is to be performed, the thickness of the pattern of protrusion portions formed by the magnetic layer of the master medium is made thin. Because the magnetic pole distance generated to pass a magnetic field through vertically is short (diamagnetic field), and there is no assistance from adjacent protrusion portions in constraining the magnetic flux between protrusion portions, etc.; it is difficult to realize sufficiently favorable signal quality by providing a soft magnetic layer having a simple form.